Seismic streamers are commonly towed by a seismic vessel in a marine environment such as an ocean. The seismic streamers record seismic signals resulting from sound waves that are mechanically generated and sent into the earth beneath the marine environment. Each seismic streamer includes a series of geophones or hydrophones that receive the seismic signals and convert them into electrical signals or some other form of signals. Because seismic streamers can be several kilometers in length, they are generally not extended in straight lines from the vessel, but rather in curved lines that may be determined by several factors such as wind speed and direction and marine current speed and direction.
Each seismic streamer may also include magnetic compasses spaced at intervals along the streamer. Each compass can measure the direction of the earth's magnetic field at certain time intervals and transmit the measurements to the seismic vessel where they can be recorded along with the seismic signals from the hydrophones. By knowing the location of each magnetic compass in the streamers and the individual compass readings, the graphic shape (including distances) of each streamer can be estimated over time. From the graphic shape, the location of each hydrophone with respect to the seismic vessel can be determined. Hence, the seismic signals received by each geophone can be precisely correlated to a position on a marine chart in order to provide an accurate depiction of the earth beneath the marine environment. Unfortunately, anomalies in the earth's magnetic field may cause the measurements by the magnetic compasses to be off by a factor based on the severity of the anomalies as compared to the magnetic north on the marine chart. Errors in measuring magnetic north with respect to the marine chart may then lead to errors in correlating the locations of where the seismic signals were received to locations on the marine chart. This may be particularly problematic near the magnetic poles or in high latitudes. It has also been seen in areas with thick ocean bottom lava flows or abducted basalt section in sedimentary accretion wedges.